In last decades, processes of obtaining liquid hydrocarbons from natural and associated gas, so-called GTL processes, attract attention of researchers and investors as an additional source of liquid fuels, lubricants and raw materials for organic synthesis. Such processes include a stage of obtaining synthesis gas and a stage of synthesis of hydrocarbons from synthesis gas in the Fischer-Tropsch process or from methanol or dimethyl ether in the MobilOil and Haldor Topsoe processes. Close integration of stages of a GTL process, utilization of new catalysts and technologies allow to improve economic performance of production of liquid hydrocarbons from gaseous raw hydrocarbons and to exploit GTL processes on remote oil and gas fields for the sake of rational use of natural resources.
Partial oxidation of raw hydrocarbons in the presence of free oxygen and water steam is the most promising method for obtaining synthesis gas. It allows to get an at least partially heat-balanced process as far as free oxygen oxidation is an exothermic process and steam reforming of hydrocarbons is an endothermic process. Besides that, combining these methods of oxidation it is possible to control the composition of synthesis gas, the ratio of its main components CO and H2. There are air, including enriched with oxygen, and pure oxygen used as a source of molecular oxygen.
As far as the second stage of GTL process is concerned, the rationale for choosing of a particular variant depends on many factors. In any case, for 1 mole of CO being converted to hydrocarbons there is formed 1 mole of water and a small amount of by-products—oxygenates (oxygen-containing hydrocarbons). After cooling and condensation of liquid products of synthesis of hydrocarbons stage, the water formed is divided from hydrocarbon products by separation. This supplementary water contains dissolved hydrocarbons and oxygenates. For example, supplement water of a Fischer-Tropsch process contains 0.02% wt. of hydrocarbons, 0.09-1.41% wt. of acidic oxygenates, and 1.00-4.47% wt. of non-acidic oxygenates depending on Fischer-Tropsch process conditions and a catalyst used (U.S. Pat. No. 7,147,775). The content of oxygenates can be especially high, up till a few percent, in reaction water of MTG and TIGAS processes of methanol and dimethyl ether conversion to hydrocarbons because it partly contains the unconverted feed components. Utilization of reaction water is connected with cleaning it up from solid particles, dissolved gases, hydrocarbons and oxygenates, and, in some cases, with cleaning it up from metal ions as well.
There is a known method for hydrocarbon obtaining by means of steam reforming of hydrocarbon feed and the Fischer-Tropsch reaction according to U.S. Pat. No. 7,323,497, in which steam for steam reforming and impoverished in oxygenates water are obtained: reaction water is heated up, and feed gas is saturated in a saturator with water steam and oxygenates that are contained in the water and form with it a low-boiling azeotropic mixture. Cleaning up the water with a low content of impurities is less expensive. It is a preferable method for all the water being formed in synthesis of hydrocarbons.
There is a known method of utilization of the supplementary water being formed during the stage of synthesis gas production and/or synthesis of hydrocarbons in the Fischer-Tropsch process from patent RU 2433085, in which the supplementary water is being treated, deairated and then used as a boiler feed, with oxygenates being removed at the stage of water treatment by at least one of the following methods: biological treatment, adsorption, membrane separation.
The most close to the given invention method of treatment and utilization of reaction water is disclosed in application WO 99/15483 for a method for obtaining liquid hydrocarbons from raw hydrocarbons. One of the variants of the prototype method comprises obtaining synthesis gas in the process of partial oxidation of feed in the presence of an oxygen-containing gas and water steam and/or water, quenching of obtained synthesis gas by injecting water in hot synthesis gas to decrease its temperature to 100-500° C., preferably to 300-400° C., its further cooling in indirect heat exchangers to a temperature of 40-130° C., preferably to 50-100° C., and condensation of water steam, dividing water condensate from synthesis gas, conversion of synthesis gas in the Fischer-Tropsch process to gaseous, liquid hydrocarbons and water, which is used in the process of partial oxidation of the feed and quenching of synthesis gas, and using gaseous hydrocarbons and water after synthesis gas quenching for electric-power generation. The electric power is used to produce oxygen.